Digital Video Broadcasting-Handheld (referred to as ‘DVB-H’ hereinafter), one of the digital broadcasting specifications for the mobile TV, is a technical specification specifying the broadcasting service specifications for the mobile handsets.
DVB-H specifies additional requirements for the handheld devices in Digital Video Broadcasting Terrestrial (referred to as ‘DVB-T’ hereinafter) which is a specifications for digital terrestrial mobile broadcasting. DVB-H was formally adopted as European standard in 2004, and details are specified in ESTI EN 302 304. In 2008, DVB-H was officially endorsed by the European Union as the preferred technology for terrestrial mobile broadcasting. Meanwhile, DVB-SH (Satellite to Handhelds) and DVB-NGH (Next Generation Handheld) are considered for possible enhancements to DVB-H, providing improved spectral efficiency and better modulation flexibility.
In general, test or measurement devices of the communication system should suffice various requirements according to the testing purpose of the user. As communication systems are tend to be more complex and advanced, performance test equipments for such systems are required to perform accurate and reliable performance testing and have measurement functions for the various test items for the communication systems.
Besides, to have more reliable test results for the various test items, same characteristics must be maintained over the various frequency ranges throughout the test. Although test equipments include various RF characteristics, uniformity of the frequency characteristics can be obtained through the following calibration process. As for the measurement equipment calibration methods, there are frequency calibration, output power level calibration, IQ modulation calibration, and modulated carrier calibration etc. The output power level over the frequency range is a barometer representing the accuracy of a DVB-H system; the reliability of the accuracy of the output power level is obtained when the continuous wave (referred to as ‘CW’ hereinafter) and the modulated wave that is the CW carrying digital data, are all maintained at the preset power level.
FIG. 1 is a block diagram of a conventional DVB-H test equipment. As shown in FIG. 1, the conventional DVB-H test equipment 100 is comprised of a baseband signal generation unit 110, a carrier generation unit 120, and a test signal modulation unit 130.
In the configuration described above, the baseband signal generation unit 110 is comprised of an I-mode signal generation circuit, a Q-mode signal generation circuit, and a gain control circuit for controlling the gain of the I-mode and Q-mode signals. The carrier generation unit 120 is comprised of a carrier generation circuit and a gain control circuit for controlling the gain of the carrier generation circuit. The test signal modulation unit 130 is comprised of an offset control circuit for the I-mode and Q-mode signals and an IQ modulation circuit. The IQ modulation circuit modulates signals by controlling the amplitude and phase of the two orthogonal signals, I-mode and Q-mode.
Meanwhile, in the DVB-H test equipment 100 as shown in FIG. 1, a RF connector 160 is mounted on the front panel 150, and the output of the test signal modulation unit 130 and the RF connector 160 are connected through the RF cable 140. In a test equipment having such structure, although it is self-calibrated up to the test signal modulation unit 130, the frequency dependent loss occurring in the RF cable 140 must be compensated.
FIG. 2 is a graph showing power loss occurring in the RF cable of the DVB-H test equipment. As shown in FIG. 2, the cable insertion loss increases as the frequency increases; since it is self-calibrated up to the test signal modulation unit 130 as described above, only the power loss occurring in the RF cable 140 between the test signal modulation unit 130 and the front panel 150 needs to be calibrated.
Meanwhile, since the power loss of the RF cable 140 is different between the continuous wave and the data-carrying modulated wave, conventionally the starting frequency, stop frequency, frequency step, and desired power level are preset individually, for example, 100 MHz for the starting frequency and 4 GHz for the stop frequency, 10 MHz for the frequency step and −25 dBm for the desired power level; thereafter the power loss calibration of the RF cable for the continuous wave and the power loss calibration of the RF cable for the modulated wave are performed separately by increasing the frequency with the frequency step, thereby requiring significant amount of time in the calibration process. Moreover, such problems are getting worse as the interval between the start frequency and stop frequency becomes wider and as the frequency step becomes smaller.